Doug,
Not being in an academic environment
with access to journals and not being able
to afford costly internet access to them,
given the attitude of academic publishers
(how many thousand bucks a year?). I
don't even have a decent library to use.
although I sometimes drive
I'm restricted to my own big messy stacks
of books, xeroxes, etc. I didn't (don't)
have Koeberl's paper itself.
I am quoting Koeberl (sorry for the
name typo) from Guy Heinen's book on
Tektites. He gives a table of F, B, and
ratios which he attributes to the Matthies
and Koeberl 1991 paper and a Chaussidon
and Koeberl 1995 paper in Geochem.
Cosmochem. Acta 59, combining them
into one table, with 14 different tektite
and impact glass types, with maybe
20 samples, but I'm not typing the
whole thing out... That's where
the data not in the 1991 paper
came from.
I think "come clean" is a bit too strong,
but you're right; the boron column in his
summary table has a blank for the moldavite.
I see that I said otherwise when you
questioned the F/B thermometer idea.
I scanned down the column and pulled
median values (instead of the full ranges
for each entry). Too quick and sloppy.
Mea culpa.
You seem to object to the entire notion
of F/B as a thermometer. OK, but don't
kill the messenger. Heinen presents it
as an accepted technique. I just read
his book. I think fluorine alone is
significant.
Again, reading Heinen, he gives from
Wedepohl values for various types of
terrestrial rocks. They all have relatively
high values for fluorine. Even the lowest
values (for ultramafic rocks) are 100 ppm,
and they range up to 1000 or more for
averages on other, more common types.
The typical values for sandstones are
180 to 450 ppm. Although I have no
values for the Nubia sandstone, I find
by Googling lots of references on problems
with the nomads and their water wells
because of "so high a content of fluorine
as to make it unfit for human consumption..."
I can't get to any geology papers on
the Nubia sandstone without paying
the big bucks...
And they're mostly about OIL,
big surprise, huh?
* fluorine values (from Heinen,
from Wedepohl)
granites 800 ppm
alkalai riocks 1000 ppm
sandstone 180-450 ppm
slate 290-800 ppm
ultramafic 100 ppm
* boron values (same)
plutonic rocks 10 ppm
sendimentary 85 ppm
ocean sediments 850 ppm
Now, fluorine sticks good (strong
bonds) and is very hard to get rid of
or clear out of a substance. That much
I know. That tektites show values of
6, 7, 8, 20, or even 30 (moldavites)
says to me that something had to
deplete them seriously of fluorine.
I don't of any other way to drive
fluorine out of a rock than to heat it.
Do you?
I also think it's significant that the
lowest fluorine values are for tektites
from the australoasian kind. They're
the youngest and have been exposed
to the terrestrial environment the
shortest time. I think that 30,000,000
year old tektites may have picked up
some fluorine from earthly ground
water in all that time. Fluorine gets
into everything... Ideally, I'd like
to see them get a fluorine reading
from a big bediasite, abrade the outer
5 mm from it, and then measure it
again. Belt and suspenders...
I think that low fluorine content
by itself tells you something about
how nasty a beating a rock got. And
you don't need 38,000 deg. to have
a plasma. Even at a measley 6000
or 8000 C, all you've got is a bunch
of screaming electron-stripped
atoms bouncing around like crazy...
More "heat" just means higher
velocities for everybody who
comes to the dance.
All the impact guys say a plasma
of 50,000 deg. or more is perfectly
normal for a big impact, for a while
anyway, there being nothing to contain
it beyond the inertia of the material,
so there's enough heat. In any impact.
Doesn't explain why only some big
impacts produce tektites, does it?
The production mechanism is still
a mystery.
You say, "neither water, nor silicon
dioxide the base material of tektite glass
would survive..." Dead right. Here's the
weird thing: while tektites are "produced"
by impact in lands all over the globe
in all kinds of geological strata, they are
monotonously alike. One chemist (Chao?)
said that analyzing tektites in big numbers
was the most boring thing he ever did,
because they're ALL blanking alike.
Their similarity can be explained in
either one of two ways:
a) the process of producing them
transforms ANY terrestrial material into
the same resulting composition by
eliminating some atoms and enhancing
the numbers of others. Not so unreasonable.
The process seems to get rid of water,
a universal component of all terrestrial
materials. Not kind to fluorine, either.
Only tough stuff is left. The oxygen
(from the water?) seems to end with
silicon (and aluminum and calcium and
magnesium, etc) as partners. Still, no one
has completely elucidated it as a process,
and it's hard to account for changes in
the population of heavy "refractories."
And the bulk compositions of target rocks
and "their" tektites do not match well
for all elements in ways hard to explain.
Paradoxically, the target rocks DO
produce impact glasses at the same
time and place; there are many varieties
of impact glasses at Ries, in addition to
the famous tektites, same for other sites.
The chemistry of these impactites do
not match the tektites from the same
location. Hmm.
b) Tektites are all the same because
they are formed entirely from one specific
type of impactor (of which, for some
reason, we have no other samples, and
not at all from the local target rocks.
End of story.
Anyone want to shave this puppy, or
is that "greased pig," with Occam's Razor?
Koeberl? Nah, let's just read his paper
to get it in writing: "The low F and B contents
in LDG and Aouelloul impact glasses are most
probably due to low contents in the
precursor materials."
Koeberl's "most probably due" sounds
suspiciously like he didn't test the source rock,
or look it up either. I translate "most probably
due" as "I guess." Doesn't sound like hard
data to me. He doesn't say, "Since Rock X
has F/B vaues of xxx/yyy..." or even "The
report of Messrs, A, B, and X give xxx ppm
for..." He doing the bread-and-butter thing,
writing a paper; if you have data, you use
it. But beyond that, arguing away some
parts of the results as due to characteristics
of the source rock ASSUMES that the
"source" rocks are the source of tektites,
but that's one of things we're trying to find
out, isn't it? Well, isn't it?
Oh, and BTW, lighten up, Doug. People
will still be arguing about tektites long after
we're both dust, you know.
Sterling K. Webb
---------------------------------------------
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
<Meteorite-list@meteoritecentral.com>
Sent: Monday, March 06, 2006 2:47 PM
Subject: Re: [meteorite-list] Largest Crater in the Sahara Desert and LDG
Sterling W. writes:
<<Doug, the actual language Kroeberl uses
is that the F/B ratio of tektites "should tend
toward 1.0." This is Professional Science
Speak for "too complex to model exactly,
but most of the cows ought to stampede
in this direction...">>
Hola Sterling, I asked you where you got the moldavite value for boron.
You
are now a primary source on the Internet saying that moldavites have this
content and some tektite man at some place like lpi may believe you... It
is very
tedious to measure boron apparenty by spectrophotometric methods - it
would
be a fair question to ask you how you got it...Slap me, call me insulting,
do I
really deserve it because it sure sounded to me you might have invented
the
"typical" value of Boron=30 ppm in moldavites and pass it off as a
"typical"
number for moldavites because you got caught up in a roll fitting numbers
to
produce a 1.0 ratio you were trumpeting - when you had no such data. If I
am
wrong please forgive me enough to be on speaking terms, and if I am right,
please
come clean.
Let me say I am much more comfortable with this last post you made than
the
prior last off-the-wall statements about tektite formation at 34,000
degree
(you really did say this, I read all of your posting) plasma-formed
tektites
miraculously being heated in microseconds to the point where first
fluorine is
driven off to a theoretical "identical" level as boron, and then they
diffuse out
at identical rates ignoring "petty" chemical differences.
We could start with considering that at the temperature you quoted being
reached, neither water, nor silicon dioxide the base material of tektite
glass
would survive, so I think you are confusing tektites with theoretical
particle
physics over a few pitchers in the Athenaeum. I mean this in the nice
way, and
need to state it as it is the heart of my disagreement on the sloopy use
of
the data. I am really entertained by your posts generally - you are
probably my
favorite poster! But you have have mixed speculation with data here and
taken liberties to mix them and present them labeled as fact.
While Dr. Koeberl (please check the proper your spelling of your sources'
surname) may have used the word "tend" as you state above, did it occur he
just
meant that the average of a few measurements was in a ballpark of 1?
Let's not
turn this incredibly simple issue into a greased pig with talk of cows
stampeding and so forth. I don't need to sort it out with Dr. Koeberl as
you
suggested, I think his paper was self explanatory, well done though not
one of his
better ones, though it would have benefitted by someone proofreading
better the
English as to not give rise to such ambiguities in interpretation. Also,
as
I asked you to kindly clarify, and you did, the sample size as I asked you
to
clarify was tiny - I'm not gonna let you off the hook on that yet.
<<And you're right; he didn't analyze that
many samples. I wish he had more data.>>
Well, let's do better here: the paper has five "tektite" samples for which
both fluorine and boron were determined.
<<He found one ivorite with a F/B ratio of
0.40 (means more boron than fluorine).>>
Yes, he did. And you can't discount it. It was one of only five samples.
Call it an outlier if you wish. But it totally nukes your wishful
morphing-random walking diffusion plasmoid theory and imaginative
mechanisms which you
presented as fact.
<<Most results were 0.8 to 1.2, which
indeed is a 'tendency" toward 1.0,
if you think numbers have tendencies.>>
I don't think the numbers have tendencies in the sense you used them to
build
an astounding physicist view. I think numbers are cold and cruel. Let's
look at the tektite numbers in the paper excluding the Muong Nongs as the
authors
suggest:
[F]/[B] ratios
Thailandite 1 1.2
Thailandite 2 1.5
Bediasite 1 0.8
Ivory C. tek. 1 1.2
Ivory C. tek. 2 0.4
Tending to 1.0? "Professional science speak" huh? No, no, no and no.
Sorry, but no. I'd go for "Settle in the ball park of 1.0", provided no
one uses
Sterling's logic to shove Fluorine and Boron into one ball, and provided
that
no one saying and implying that these molecules or elements coordinate
themselves to reach equal levels in time to loose their identies only to
regain them
again...
Degreasing the pig, let's grab a hold of it and cut to the throat of the
issue. You originally argued that LDG's were extremely hot like tektites
pointing
to this fluorine-boron "thermometer" and told us without references that
the
fluorine and boron values were 7 ppm each in LDGs, arguing that this made
them
comparable to heat for tektites, and that the low absolute ppm numbers
(which
were lowers than most tektites, btw). You said that geochemists were
behind
this, not friendly physicists, and that all of this is established
protocol
for geo- and cosmo-chemists. You pointed to your theories of formation of
tektites and then said this whole thing was not hatched by you. In fact,
it was.
A more careful reading of the paper, and you will find that besides the
1.0
[F]:/[B] ratio for LDG which you attributed so much significance to, there
was
a second LDG studied in the table, too:
[F]ppm, [B]ppm, [F]/[B] ratio
LDG 1 7, 7, 1.0
LDG 2 8, <5, *
Well, the second sample had no ratio reported. But: it is clear that
sample
2 has a ratio GREATER THAN 1.6 for [F]/[B]. How much GREATER? Maybe a
lot.
Maybe a little, we don't know though. (though I could speculate <5 means 4
or
less, so we are in the 2.0 or higher index). Note aside: there was also a
second Bediasite with coincidentally equal B and F ppms as the LDG 2. So
its
ratio was actually GREATER THAN 1.6 or 2.0, too.
Then there are the absolute numbers to deal with. The low value of "7"
you
attributed AS FACT to the incredible heat of formation of LDG's (while you
brushed off the contradictory water content and inclusions)? Well, as you
see, it
might be 7, it might be 8 or it might be 4, etc. They are all quite low,
though. Let's not read into the data more than it allows, nor look to
geologists
for a better "thermometer" yet. How about asking Dr. Koeberl? Nah, let's
just read his paper to get it in writing:
"The low F and B contents in LDG and Aouelloul impact glasses are most
probably due to low contents in the precursor materials."
At no point in Dr. Koeberl's paper does he support the fantastic boron &
fluorine mechanisms you have imagined - he, like I have stated, simply
says that
Fluorine will be preferentially outgassed during random diffusion. No
looking
for the magic level, no going down together in unison, good grief. He
seems
to be suggesting that anyone wanting to know more explanations should look
to
the source rock - which is what I said in my original objection refuting
your
claims about extrapolating with the "thermometer"..
No one argues that all impact glasses aren't hot, not even me. LDG's also
have a somewhat layered microstructure and the 2.0 is up into the Muong
Nong
range now, for what its worth (not too toooo much, of course...) Now with
that,
die bad theory! Resurrect thyself from the lab and field and not the
armchair...
It is much more palatable to me to view the approximate ratio as a very
general concept where a splashform will have a lower value than a Nuong
Nong from
the SAME source material. These comparisons in the lab are hard enough
for the
same event,let alone different ones - and that the measured range is 0.4
to 5
for a few tektites and impact glasses. Let me now comfortably settle back
into my armchair and congratulate everyone involved in the research
efforts, as
well as the "babblers" (not my word, but I find sometimes irony them out
works!)...
Saludos, Doug
PS I'm still hoping to know the values of [F] and [B] in the LDG country
rock...maybe Norm or some other real geologist out there has them in a
geology
handbook?
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